Fixing device having a heat supply part and image forming apparatus

Abstract

A fixing device includes an endless belt. A heat supply part is disposed inside the belt, contacts an inner circumferential surface thereof, and supplies heat thereto. A pressure member contacts an outer circumferential surface of the belt to form a nip portion, and conveys a recording medium while nipping the recording medium together with the belt. The heat supply part includes a heater having a plurality of heating sections arranged in a widthwise direction of the belt, and a thermal diffusion member extending in the widthwise direction between the heater and the belt. One surface of the thermal diffusion member contacts the inner circumferential surface of the belt, and the other surface contacts the heating sections. A plate thickness t (mm) between the surfaces of the thermal diffusion member, and a thermal diffusivity D (mm2/s) of the thermal diffusion member satisfy the relationship: t×D≥6.7.

What is claimed is: 
     
       1. A fixing device comprising:
 an endless belt; 
 a heat supply part that is disposed inside the endless belt, contacts an inner circumferential surface of the endless belt, and supplies heat to the endless belt; and 
 a pressure member that contacts an outer circumferential surface of the endless belt to form a nip portion, and conveys a recording medium while nipping the recording medium together with the endless belt, 
 the heat supply part comprising: 
 a heater having a plurality of heating sections arranged in a widthwise direction of the endless belt, and 
 a thermal diffusion member that extends in the widthwise direction between the heater and the endless belt, and is disposed so that one surface of the thermal diffusion member contacts the inner circumferential surface of the endless belt, and the other surface of the thermal diffusion member contacts the plurality of heating sections, 
 wherein a plate thickness t (mm) between the one surface and the other surface of the thermal diffusion member, and a thermal diffusivity D (mm 2 /s) of the thermal diffusion member satisfy the relationship:
     t×D≥ 6.7. 
 
 
     
     
       2. The fixing device according to  claim 1 , wherein the thermal diffusion member comprises a cover layer covering the one surface. 
     
     
       3. The fixing device according to  claim 2 , wherein the thermal diffusion member is made of stainless steel (SUS) and the cover layer. 
     
     
       4. The fixing device according to  claim 1 , wherein the cover layer is made of glass material. 
     
     
       5. The fixing device according to  claim 1 , wherein the plate thickness t satisfies:
   0.5 mm≤ t.  
 
 
     
     
       6. The fixing device according to  claim 1 , wherein the plate thickness t and thermal diffusivity D satisfy:
   6.7≤ t×D≤ 12.0.
 
 
     
     
       7. The fixing device according to  claim 1 , wherein the plate thickness t and thermal diffusivity D satisfy:
   6.7≤ t×D≤ 10.7.
 
 
     
     
       8. The fixing device according to  claim 1 , wherein the heat supply part comprises a holding member and a heat retaining plate,
 wherein the heat retaining plate is disposed on a side of the heater opposite to the thermal diffusion member, and 
 wherein the holding member and the thermal diffusion member sandwich the heater and the heat retaining plate. 
 
     
     
       9. The fixing device according to  claim 8 , wherein the thermal diffusion member has a U shape such that two ends of the thermal diffusion member in a conveying direction of the recording medium face each other, and
 wherein the holding member has a pair of regulation grooves into which the two ends are fitted so as to regulate a displacement of the thermal diffusion member with respect to the holding member. 
 
     
     
       10. An image forming apparatus comprising the fixing device according to  claim 1 .